Topic 4 - Waves

• Paritcles vibrate perpendicular to their direction of travel. • They transfer energy • They all travel at the same speed in a vacuum (3x108) • All EM waves are examples of this • Water waves are transverse

• Particles vibrate parallel to direction of travel • Areas of compression and rarefraction • Sound waves • Seismic P waves

• The amount of waves passing in a second (measured in Hertz Hz. Determines pitch or colour) • The time it takes one wave to pass a point • The length in m from one point to the next identical point of a wave • The distance in m from a waves rest position to its trough or peak

v = d/t (Velocity = distance ÷ time) v = f x λ (Velocity = frequncy x wavelength)

• Measure the distance the buoys are apart. • Record the amount of time it takes for a single wave to get from one to the other. • Do distance/time to get the wave speed.

• Set up a wave tank filled with water and a straight dipper with a ruler along the side • Vary the voltage provided to the straight dipper till there are at least 2 waves visible at any point • Count how many waves form in 10 seconds and divide by 10 to get your frequency • Using the ruler estimate the wavelength of a wave • Frequency x wavelength • Alternatively, record how long it takes the wave formed to travel a certain distance and to distance/time

• Suspend a metal rod using clamp stands • Hold a smartphone with a frequency app at one end • Hit the other end of the rod with a hammer and record the peak frequency • Meausure the length of the rod • Frequency x wavelength

• When a ray of light reaches an interface (boundary) between substances, it changes speed (because light’s speed is dependant on the density of the substance it travels in). • If it slows down it bends towards the normal and if it speeds up it bends away

• Waves of water travel faster is depper water than shallow water • They also are longitudinal so can be represented with lots of parallel lines rather than one line • When the wave of water reaches a boundary between shallow and deep, the part of each line that is furthest ahead, will reach the boundary first and slow down first. • This gradual change in which parts slow down means that the wave bends towards the normal

• Reflect: The waves bounce off • Refract: The wave passes into the new material but changes direction • Transmit: The wave passes through without being absorbed or reflected • Absorbed: The wave disappears as the enrgy it was carrying is transferred into the material

Each frequency of light changes speed at a slightly different rate meaning that at the right angles they can be split up

• Sound waves enter the ar canal which focuses it • The eardum is a thin membrance which vibrates due to the soundwaves’ vibrations • Vibrations are passed on to tiny bones which amplify the vibrations • Vibrations are passed on to the liquid inside the cochlea • Tiny hairs inside the cochlea detect these vibrations and convert them to electrical impulses • Impulses travel along the auditory nerve to reach the brain

• The cochlea has a membrane covered with hair cells • Each hair cell is connected to a neurone so that when it detects a vibration of its frequency it creates and electrical signal • The cochlea is a spiral with the outmost part (the base) detecting hgih frequencies (up to 20000Hz) and the low end (the apex) detecting lower frequencies (down to 20Hz)

• As people get older, the hairs of the base and apex of their cochlea can get damaged. • This means that they are no longer able to convert vibrations into impulses • Thus they can’t hear these sounds

20Hz - 20,000 Hz

Sound above 20,000 Hz

• To find the depth of the water beneath them. • They fire off an ultrasound wave at 1500m/s. • They time how long it takes to return. • They use d = s x t to find out the distance hte wave travelled and divide it by 2 to find the depth of the water

• A probe emits ultrasound waves • Gel is used to stop it from reflecting • Some waves are reflected when they meet bones, fat, tissue etc. • The probe also detects these refelected waves • It sends these as impulses to the computer • The ultrasound imaging machine detcts the frequency of the impulses turning it into an image

• Other scans such as PET and CT would release radiation • This could harm the foetus causing mutations

Sound below 20Hz

• P waves: Longitudinal • S waves: Transverse

Vibrations produces by earthquakes

• P waves are longitudinal while S waves are transverse • S waves can only be transmitted by solids but P waves can go through all through states • The earth has a liquid outer core • S waves fired from a point can’t go throuhg the liquid core but P waves can • This means that S waves have a larger shadow zone • Using the idea that S waves can’t go through liquids and P waves can, scientists were able to find out about the structure of the earth

The area where a wave cannot reach when fired from a point